Alcohol addiction is a devastating condition perpetuated by enduring physiological and behavioral adaptations. At the core of these adaptations is the long-term rearrangement of neuronal gene expression in the brain of the addicted individual. However, the mechanisms by which alcohol consumption produces this rearrangement and leads to lasting changes in behavior remains unresolved. Epigenetic histone modifications have recently emerged as important modulators of gene expression and are thought to represent a form of transcriptional memory that is directly imprinted on the chromosome. Some histone modifications affect transcription by modulating the accessibility of the underlying DNA while others have been proposed to serve as marks read by transcription factors as a 'histone code' that helps to specify the expression level of a gene. While the effects of some epigenetic modifications on the transcriptional activity of genes is well known, little is known about the temporal dynamics of these modifications and their relative contribution to the initiation and maintenance of alcohol-induced transcriptional changes. The objective of this application is to investigate the temporal role of epigenetic modulators underlying long-term functional alcohol tolerance ?a key component of the addictive process. In flies, a single alcohol sedation induces a tolerance phenotype that lasts over 10 days. This phenotype is a direct product of neural adaptations to the drug that also give rise to equally lasting withdrawal symptoms. The central hypothesis is that acute exposure to alcohol causes a sequence of lasting changes in histone modifications that lead to the reprogramming of the brain transcriptome. Different modifications are believed to have distinct effects on the initiation and/or the perdurance of alcohol tolerance. To test this hypothesis, this proposal combines a thorough examination of histone modifications with the power of Drosophila genetics to identify and characterize the epigenetic modulators that contribute to the temporal dynamics of tolerance to alcohol. A comprehensive survey of alcohol-induced histone modifications will be performed on flies that have been exposed to alcohol. Different time-points will be assessed in order to capture the entire span of the alcohol-tolerance phenotype. In parallel, the activity of independent histone modification enzymes will be manipulated in the fly nervous system to determine their contribution to the dynamics of this phenotype. Finally, targeted removal of epigenetic marks at specific candidate gene loci will be performed in an attempt to revert the development of tolerance to alcohol. Achieving these goals will help identify and evaluate the temporal role of epigenetic histone modifications on the neural adaptations that underlie alcohol tolerance and will contribute to the understanding of how alcohol consumption perpetuates changes in expression that promote addiction. Targeting these regulatory mechanisms rather than individual genes will result in a more effective therapeutic strategy for reversing global alcohol effects relevant to drug addiction.